The change in legislation is designed to protect children and young people aged under 18 from the damaging effects of secondhand smoke.
The new law applies to any private vehicle enclosed wholly or partly by a roof, even if the window is open, the air conditioning is on or the smoker is sitting in the open doorway of the vehicle.
Research shows second hand smoke can put children at risk of serious conditions such as meningitis, asthma, cancer, bronchitis and pneumonia.
As from March 31, it will be an offence for anyone aged 18 or over to smoke in an enclosed motor vehicle when there is a child in the vehicle and the vehicle is in a public place.
The new legislation follows the Smoke-Free Environment Act 2012, which made it an offence to smoke in enclosed public places and in public service vehicles in Gibraltar.
Similar legislation is already in place in UK, France, South Africa, much of Australia, Canada and the USA and several other countries.